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FIELD REPORT FOR GEOLOGICAL EXCURSION TO
DECCAN TRAPS, PUNE,
INDIA
PURUSHOTTAM GUPTA
INT .MSC . EARTH SCIENCE
6 SEMESTER
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ACKNOWLEDGEMENTS
I would like to thank Prof. M.Jayananda & Prof. G.V.R. Prasad
for giving us the opportunity to work on Deccan Basalts during
this field trip.
I would also like to thank Dr.Raymond Duraiswami & all the
faculty of Geology Department,Pune University for guiding us
in the field .
I would also like to thank our classmates for their valuable
contribution and help in preparing this report.
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INTRODUCTION
Global distribution of large igneous provinces (shown in black)
The beginning and the end of the Cretaceous period in India witnessed
voluminous outpouring of lavas and stupendous volcanic explosions. In the early
Lower Cretaceous (114-118 Ma), nearly 20,000 km² area of eastern India
embracing the Rajmahal Hills in Jharkhand and the Sylhat region in Meghalaya
was affected by volcanism. Towards the close of the Cretaceous (61 to 69 Ma),
more than 500,000 km² land in western and central India was inundated by
extensive floods of lavas. The eastern theatre of volcanism is known as the
Rajmahal Volcanic Province and the western domain as the Deccan Volcanic
Province . The Deccan Volcanism was preceded by eruption of lavas 91-95 Ma ago
in offshore north-western Karnataka, giving rise to the Saint Mary's Islands. In the
Rajmahal Volcanic Province the lava pile was nearly 244 m thick, while the lava
succession is more than 2,500 m in the Nasik district in Maharashtra in the Deccan
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Volcanic Province.
The Deccan lavas are believed to have flowed 100-300 km from their sources
along the Western Ghats and in the Narmada Valley, before they froze to form
stepped plateaus. Evidently, the lavas must have been very mobile and, therefore,
spread far and wide, overcoming topographic impediments, filling depressions
and valleys, damming rivers and streams, and burying forests and grasslands. The
result of the lava floods was the evolution of flat-topped plateaus, with step-like
landform called the Deccan Traps. The Deccan Volcanic Province covers
Maharashtra and adjoining regions in Gujarat, Madhya Pradesh, Andhra Pradesh,
and Karnataka.
One among the most remarkable volcanic provinces on earth, the Deccan
Volcanic Province (DVP) is a very prominent terrane of the Indian subcontinent.
The name Deccan Traps was given by E. Vrendenburg, 1908. Outcrops of the DVP
in distant Rajahmundry in Andhra Pradesh and in Kachchh and Saurashtra in
Gujarat indicate that the extent of the DVP was much larger in the past. Offshore
drilling west of the Konkan Coast revealed subsurface extension of the Deccan
lavas in the Arabian Sea. In some places the top of the larva lie nearly 1,500 m
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below the sea level, pointing to the foundering by faulting of the western part of
the DVP.
Nature of Deccan Lavas
The bulk of the Deccan lavas are tholeiite basalts of simple type. In addition to
basalts, the other rock types of the DVP are alkali basalts (basanite and picrite).
nephelinites, carbonatites and rhyolites. occuring in minor amounts in the rifted
western margin of the domain and in the Narmada Valley. In the Sahyadri Range
the lava buildup comprises dominant pahoehoe flow fields. These are aggregates
of many flow lobes, each of which grew by thickening through injection of melt
under solidified crust .
Thin irregular flows with ropy surfaces dipping in different directions, and piled up
into chaotic masses, are quite common in western Maharashtra .The Bor Ghat
section along the Pune-Mumbai tract provides a portrait of the variable
morphology, structure and texture — thick extensive flows of compact basalt,
tabular flows of amygdaloidal basalt, thin irregular flows of amygdaloidal basalts,
and thin irregular flows of vesicular basalt .It seems that in the early stage, viscous
lavas erupted in small quantities, and later there was fissure eruption in the
Mumbai-Pune region. East of Pune near Daund, a hummocky flow with toes,
lobes toccatas and lava tubes characterize are terminal part of the Thakurvadi
Formation. (Valdiya,2010}
Lavas of CFB
• Lithosphere is below continents
• Continents have refractory roots
• In super plume events,continents fragment.Thus,CFB can be formed by plume impacts or
astroroid impact.
• DVP lavas are enriched .Higher incompatible elements.
• Higher LREE & Lower HREE indicated it is not depleted.
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Lithostratigraphy — Magnetostratigraphy
On the basis of detailed studies in the Mahabaleshwar-Nasik region in
Maharashtra, involving interpretation of measured sections,
palaeomagnetism, analyses of major and trace elements in rocks, and
determination of isotopic ratios of rare earths and strontium, a
standard stratigraphy of the DVP has been established .The DVP lava
succession is divisible into four subgroups comprising fifteen
formations, each distinctive in its chemical types. The younger
formations have wider spread - the Poladpur Formation lavas extending
800 km northwestwards to Gujarat and northwards to Madhya
Pradesh, and the Mahabaleshwar lavas reaching as far south as Belgam
in Karnataka. It may be stressed that the lava flows are not continuous -
there is pinching and swelling along their spread. There is also
southward overstepping of successive units such as the Bushe
Formation tapering out near Lonilind, and the Khandala Formation
resting directly under the Poladpur. The upper Wai Subgroup makes up
the entire southern part of the DPV, overstepping all older formation
southwards, the Mahabaleshwar Formation overstepping the
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Precambrian rocks of Belgam, and so on.{Valdiya,2010}
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COMMON TERMS & TERMINOLOGIES
Simplified definition of lava types and their morphology. Note that all the sketches are along the
longitudinal section
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Distribution of predominantly pahoehoe /compound and a`a/ simple flows in the Deccan Volcanic
Province
Compound lava flows, defined as those lavas which are divisible into flow. units,
commonly have a shield-like form and are thought to develop when the rate of extrusion
of lava is relatively low.
Simple lava flows, defined as those lavas which are not divisible into flow-units, are
thought to form when the rate of extrusion of lava is relatively high.
• All information in points is from field notes.
• All information in paragraphs & sketches are from various research journals.
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THE FIELD
Our field trip was mostly centered around the city of Pune within a radius of 100 km .The weather was
sunny ,clear & comparatively hot with temperatures reaching upto 30°C from 12 December 2012 to 15
December 2012
Day 1
Diveghat
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Compound pahoehoe flow with predominant vesicles (left bottom) .Field sketch of compound pahoehoe flow unit
(right top) . Sketch of part of a flow lobe at DiveGhat (right bottom). A,B, C, and D refer to the crust, zone of elongated
vesicles, jointed core, and segregation veins respectively.
• Zeolite minerals like Stilbite & green earth also found. Horizontal vesicle banding seen
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A few metre away a dike was recorded.
Chilled margin (left) & dike offshoot (above)
Dike is easily identifiable from difference in colour &
differential jointing pattern from rest of the rock body.
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Diveghat Site 2
Bushe formation. Hummocky flows
• Exposed Bushe Fm show hummocks & spheroidal weathering.Flow direction is towards NWW
Photograph & Field sketch of flow lobes exposed along the road cut in Diveghat Note the termination of lobe 2 against lobe 4. Only the upper crust of lobe 4 is exposed, while the basal crust, crudely jointed and spheroidally weathered core, and part of upper crust of lobe 1 are exposed.
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Diveghat Site-3
Columnar jointing seen(not very prominent).Poladpur Fm.Typical colonnade/ entablature
structures seen.Simple flows have lots of columns.Some plumose jointing also seen.
Simple flows in the DVP generally can exhibit well-developed jointing patterns. These patterns are
generally persistent laterally and are referred to as colonnade and entablature .Entablature refers to
0.30- to 0.50-m- thick, irregular columns that occur in the upper portions of flows. They commonly
deviate from a perpendicular orientation and may form radiating patterns. In certain flows, two or
more levels of entablature are seen, usually separated by platy joints .Well-developed colonnade
structures are usually seen in the lower portions of most simple flows. Columns are commonly
perpendicular to the base of the flow and their width ranges from 0.50 to 2.0 m. An upper
colonnadezone is also present in some flows. The entablature is often glassy and sometimes shows
horizontal vesicular zones. In other flows, no clear distinction between the colonnade and
entablature can be made, and the entire flow shows highly irregular jointing and a fine texture. Good
examples of entablature and colonnade structures are seen at southern parts of the Western
Ghats(Katraj Ghat, Dive Ghat, Mahabaleshwar, etc.)(Bondre et al,2004)
Photograph & Field sketch of a simple flow exposed in
Dive Ghat .A refers to the entablature, a zone of
randomly oriented jointing that imparts a chaotic
appearance to the zone.
B refers to the colonnade, characterized by more regular
columnar joints.
Entablature is probably the result of cooling caused by
fresh lava being covered by water. The flood basalts
probably damned rivers. When the rivers returned the
water seeped down the cracks in the cooling lava and
caused rapid cooling from the surface downward. The
division of colonnade and entablature is the result of
slow cooling from the base upward and rapid cooling
from the top downward.
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Diveghat
Site-4(site-3 + 200m)
Flow top breccias of compound flow seen.Bunline & crust also seen (red)
Sketch of small, bun-shaped pahoehoe lobes exposed along road cut
Angular rubble blocks occurring near the upper surface of
a typical a`a flow exposed in Diveghat area, Pune district
Photo courtesy-G.S.I.
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Purandar Fort
Site-5
Purandar is about 40kms south-east of Pune.
Perched on a gigantic mountain mass, its
height above sea-level is 1398 metres and
about 700 metres above the plain at its foot.
To an unaided eye, the lava flow is usually light to dark grey, fine to medium grained rock with aphyric
(without identifiable minerals) to phyric (with identifiable minerals/phenocrysts) texture. Sometimes the
rock contains crystals (mainly plagioclase feldspar-an aluminosilicate) as large as 2cm or even more and
is called a "megacrystic basalt" or "Giant Plagioclase Basalt (GPB)".
The lowest sub-group, the Kalsubai, contains a number of horizons of lavas with abundant, large tabular plagioclase crystals termed megacrysts: these are the GPBs . Individual GPB flows are 5^10m thick and occur at distinct horizons within the eruptive sequence. GPB flows were mostly sampled in road cuts and quarries, where the flows are relatively well exposed .At these locations it is clear that the GPBs are not homogeneous, but are composed of at least two magmatic components.one aphyric or sparsely phyric and another rich in plagioclase megacrysts The GPB lavas consist of plagioclase megacrysts in a finegrained matrix. The plagioclase megacrysts are 2-50mm long.( Higgins & chandrasekharam,2007)
(Clockwise from above left)Variations in the
plagioclase megacryst content within a single
GPB flow. The field of view is 40 cm.Field
photographs.Photomicrograph of the GPB flow
showing plagioclase laths.
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Model for the formation of Giant Plagioclase Basalt flows, Deccan.(Higgins & chandrashekharam,2007)
A possible history is as follows. (1) Plagioclase megacrysts crystallize in a convecting magma chamber just below the
lava pile. (2) Currents sweep the crystals to the top of the chamber, where they accumulate as a result of their
buoyancy.The crystals coarsen in response to the continuous supply of hot magma.(3) New magma sweeps through
the plagioclase mush, mingles and mixes, then erupts to form the GPBs.
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• GPB of deccan are used as Lithostratigraphy markers between bushe & poladpur
fm.(Kalsubai(U) & Wai(L) supergroup)
• 4 places in Deccan GPb are foundM1-Jowar,M2-bhimashankar,M3-Lonavala,M4-Purandar
manchar fm.Thus they are an indication of four times magma chamber replenishment.
SITE-6 (EN RO UT E PUR AN DA R) Columnar Jointing
Columnar jointing results when basalt or (other igneous rocks) cools from the outside in causing shrinkage and the development hexagonal joint structure.
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Day 2 (13.12.12)
SITE-1 SUS ROAD 1 8 .3 2 N ,7 3 .4 6 E • Mid point between Wai & Kalsubai Fm.
• Lava toe-endogenous lava growth
• No new visco-elastic thrust
• Toe inflates to lobe
• Lobes coalace to form larger lobes(sheet lobes)
• Both hummocky & sheet pahoehoe seen.
(Clockwise from top)Road cut section.
Generalized sketch of flow lobes.
Sketch of a lobe exposed
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• Massive flow has dixitaxitic texture & fine gas cavity.
• Vesicles merge at the central crack
• Lots of Zeolite minerals seen as last phase in hydrothermal activity mainly
okenite,stilbite,scolocite
A large vesicle hosting a
variety of secondary/ cavity
minerals
Blue cavenzite and heulandite,Green apophylite & stilbite. Photo courtesy-G.S.I.
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SITE-2 KATRAJ GHAT 1 8 .2 6 N ,7 3 .5 1 E • Edge of shield (volcano)
• End of Bushe Fm.
• Dyke seen.Age is 59±5 My Ar/Ar
• Younger than Bushe
• No direct feeder relation
• N5° strike.Parallel to west coast.
• Sharp,jointed ,crenulated margin
• In magmatic plumbing system,if outflow is not continous ,lava falls back as seen here.
(Clockwise from above)Margin offset & lava falling back seen.
Dyke intruding(dolerite) the previous flow.(In Magnification) Chilled,sharp & jointed margin.
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SITE-3 AMBEGAON 18 .2 5N,73.50 E (+26 Km. site2)
• Flood lava fills depression.Lava is stagnated in pool & ponded
• Convective current cause recling of the crust.
• Based on analogy of Hawaiian lava lakes.
• Features formed due to the sinking of the flow-top breccias crusts into these flows’ molten
interiors
Thick flood basalt lava flows cool conductively inward from their tops and bases, usually developing
columnar jointing. Although relatively rapid cooling in such flows due to meteoric water circulation has
been previously demonstrated, mixing of the surface crust with the interior – as observed in active lava
lakes – has not been shown. The breccia-cored rosettes described are restricted to the “simple” flows from
this province, which tend to be single cooling units of greater spatial dimensions than typical pahoehoe
lobes constituting the compound pahoehoe flows . Several simple flows are characterized as rubbly
pahoehoe i.e.,flows with extensively brecciated flow-top crusts.(Sheth et al,2011)
• Differential shear lead to platy joint like structure
Differential shear Cooling columns
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SITE-4 LONAVALA 18 .4 1N,73 .2 3E
We are
looking
here.
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SITE-5
• Transitional flowtop breccias
• Flow banding seen.Kinkery type
• Tooth paste lava(A transitional type of lava that develops within flow fields when
the lava has cooled sufficiently to have a high viscosity and when the flow is
advancing slowly.)
• Anisotropy of magnetic susceptibility
Toothpaste lava, an important basalt structural type which illustrates the transition from
pahoehoe to aa,. Its transitional features stem from a viscosity higher than that of
pahoehoe and a rate of flow slower than that of aa. Viscosity can be quantified by the
limited settling of olivine phenocrysts and rate of flow by field observations related to the
low-angle slope on which the lava flowed.(Rowland & walker ,1987)
Characteristic features of
toothpaste lava. Direction of flow
is left to right. Arrows
approximately I, 0.5, and 0.01 m
long in a, b, and c, respectively. a
Toothpaste tongue issuing from
curved bocca. S I-S2, lateral shear
zone evidenced by imbricate
shearing and clinker. Note how
longitudinal lineations maintain
same spacing along length of
tongue. b Cut-away view showing
pulse buckles (Pb) and pulse flaps
(PjJ, features of discontinuous
extrusion. Note how vesicles
deformed because crust was
retarded relative to underlying
lava. c Close up showing spines
pointing back toward
bocca.(Top)Field image.
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In Hawaii, this transitional morphological type is found at greater distance from the vent and has a rough,
hackly crust that deforms into broken plates or ropy folds. In case of toothpaste lava, the ‘ridges’ are
formed perpendicular to the flow direction and the surface grooves and striations on the surface are
parallel to the flow direction.. Moreover, it is not clear as to how an extremely viscous lava type like
toothpaste lava (viscosity: 6000–12,000 Pas) could be generated locally in a predominantly pahoehoe
flow.(Duraiswami,2009)
DAY-3 (14.12.12)
SITE-1 BHADGAON TO SUPE 1 8.25N ,7 4.1 9E
(120 KM FROM PUNE)
• Eastern Bushe(terminal)
• Pahoehoe to aa conversion
• Pipe vesicles along with breccias seen.
• Chemically the fm. is Bushebut physically transformed
• Flow correlation after 120km
• Rubbly pahoehoe
• Hulendite zone(Ca,Mg Zeolite)
The pahoehoe flow exposed in the Morgaon area probably represents the terminal parts of a larger flow
field belonging to the Bushe Formation16. It is envisaged that the lavas belonging to the Bushe Formation
could have erupted close to the crest line of the Western Ghats near Lonavala and the lavas could have
travelled eastwards to the extent of >140 km through a complex network of interconnected lobes
constituting distinct flow-fields. The earlier extent of the Bushe Formation was mapped as ending a short
distance east of Pune city.However, the present investigation and presence of pahoehoe east of Daund and
near Indapur, could indicate that the Bushe Formation could be more extensive than previously mapped.
The presence of evidence of a lava lobe preserving the evidence of pulsed inflation in the terminal parts of
the hummocky flow is significant. Based on this evidence it can be concluded that pulsed inflation could
be a phenomenon common in the terminal parts of some of the hummocky pahoehoe flows from the
Deccan Trap and can account for some of the intriguing geometry in the pahoehoe
flows.(Duraiswami,2009)
• Museum quality mineral samples found
here.
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SITE-2 KUKDI RIVER
SECTION 1 8 .1 6 N ,7 4 .1 8 E
• Ash beds from Java(Toba
caldera)
• Highly reworked by local
people
Rhyolitic tephra predating late
Pleistocene (26,000–12,000 yr B.P.)
alluvium was recognized in
Quaternary sediments of the Son
Valley, north-central India in and later
identified as having been derived from
Toba, northern Sumatra The Toba ash
occurs extensively in the Indian subcontinent and marks a ca. 74,000-yr-old event. In the Bay of
Bengal and Indian Ocean it is about 10 cm thick, whereas in several alluvial basins, it is usually
1-3 m thick. The latter occurs in a partly reworked state but as nearly chemically pure first-cycle
sediments, The ash has a broad northwesterly dispersal pattern. Samples of ash from the Indian
subcontinent compare closely with the Youngest (74,000 yr B.P.) Toba Tuff and the deep-sea
Toba ash in bulk chemical composition, REE signature, and bubble-wall shard morphology.
However, a more proximally located and thicker (2-5 m) ash-bed, from the alluvial basins in the
gneissic area and close to east coast, has a lower magnitude negative Eu anomaly, possibly
because of minor contamination by feldspathic silt. Quarternary sediments in the central
Narmada and middle Son basins contain rich late and middle Pleistocene mammalian and
cultural records. Based on the presence of the ash layer marker and stratigraphic relations, late
Pleistocene sediments within the subcontinent can be correlated with those from central India
and the deep sea. (Acharyya and Basu,1993)
Middle Palaeolithic archaeological assemblages at Jwalapuram in Kurnool district, Andhra
Pradesh, associated with 2.55 in thick layer of volcanic ash with glass shards representing the 74
ka BP Youngest Toba Tuff, indicate that humans were present in the Indian continent . The
Stone Age people must have braved the rains of volcanic dust that fell in Maharashtra, adjoining
Andhra Pradesh and in the Narmada and Son valleys in Madhya Pradesh.(Valdiya,2010)
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SITE-3 JEJURI 1 8 .1 6 N,7 4 .0 8 E
• Debris flow of alluvial formed under
gravity
• Unconformity b/w Deccan &
Quaternary.
• Metrionic diagenesis
• Nodular & concretionary calcrete
• Cementation by percolation
• Near source
SITE-4 • 16,500±500 yr bp
• Upper Pleistocene
• Mud flow overlain by
water deposit.
• Sheet flood deposit
Gastropod shells
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DAY-4 (15.12.12)
SITE-1 SHIRVAL 1 8 .0 5 N,7 3 .3 9 E
• Ambenali flow
• 1-2 metre thick flow top breccias seen with massive
core.
• Crust occurs as enclaves within cores.
• Rosette pattern seen
• Flow bottom breccias also seen
• No time gap.
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general road cut section
SITE-2 MAHABALESHWAR 1 7 .5 8 N ,7 3 .3 8 E
ARTHUR SEAT • Savitri river section
• Poladpur to ambenali transition 600m
• Ambenali to mahabaleshwar transition 800m
• Only place in the world showing triangular facets with flat topped mountain together.
Flow top breccia
Flow bottom
breccia
Rosette
cooling
pattern
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Triangular peaks to the left & flat topped mountains to the right.
• Formed due to post collisional stress buildup.
SITE-3 LATERITE DEPOSITS • Residual deposits formed in hot,
humid, climate containing lots of
vegetation, high temperature &
precipitation.
• Chemical alterarion of basalts.
• The decay of plant products
producec weak acids,which
cause alteration of primary
minerals.
• Alkalis are first to move in
solution
• Iron,TiO2 is left
• Reworked laterite is duricrust
• Oldest laterite is of Jurassic age
in India.
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Typical textbook illustration of a laterite profile . Rock structure is usually preserved in the pallid and mottled zones indicating that these zones consist of weathered rock in situ with no volume alteration.
In the Deccan region of western India ferricrete duricrusts, usually described as laterites, cap some basalt summits east of the Western Ghats escarpment, basalts of the low-lying Konkan Plain to its west, as well as some sizeable isolated basalt plateaus rising from the Plain. The duricrusts are iron-cemented saprolite with vermiform hollows, but apart from that have
little in common with the common descriptions of laterite. The classical laterite profile is not present. In particular there are no pisolitic concretions, no or minimal development of concretionary crust, and the pallid zone, commonly assumed to be typical of laterites, is absent. A relatively thin, non-indurated saprolite usually lies between the duricrust and fresh basalt. The duricrust resembles the classical laterite of Angadippuram in Kerala (southwestern India), but is much harder. The High Deccan duricrusts capping the basalt summits in the Western Ghats have been interpreted as residuals from a continuous (but now largely destroyed) laterite blanket that represents in situ transformation of the uppermost lavas, and thereby as marking
the original top of the lava pile.(Ollier and Sheth,2008)
• In India ,near sea-level laterites have age of 20 my & far from sea have age of 30-40 my
• Help in drainage pattern origin.
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REFERENCES 1. Acharyya, S. K., and Basu, P. K. (1993). Toba ash on the Indian subcontinent and its implications
for correlation of late Pleistocene alluvium.Quaternary Research , 10–19.
2. Bondre N R, Duraiswami R A and Dole G 2004 Morphology and emplacement of flows from the
Deccan volcanic province, India; Bull. Volcanol.
3. Bondre N R, Duraiswami R A, Dole G, Phadnis V M and Kale V S 2000 Inflated pahoehoe lavas
from the Sangamner area of the western Deccan volcanic province; Curr. Sci.1004-1007
4. Bondre N R, Duraiswami R A and Dole G 2004a Morphology and emplacement of flows from
the Deccan volcanic province, India; Bull. Volcanol. 29-45
5. Bondre N R, Duraiswami R A and Dole G 2004b A brief comparison of lava flows from the
Deccan volcanic province and the Columbia-Oregon Plateau flood basalts: Implications for
models of flood basalt emplacement. In: Magmatism in India through Time (eds) H C Sheth and
K Pande; Proc. Ind. Acad. Sci. (Earth Planet. Sci.) 113 pp 809-817
6. Duraiswami R A, Dole G and Bondre N R 2003 Slabby pahoehoe from the western Deccan
volcanic province: Evidence for incipient pahoehoe-aa transitions; J. Volcanol. Geotherm. Res.
121 195-217
7. Duraiswami R A ,2009 Pulsed inflation in the hummocky lava flow near Morgaon,
western Deccan Volcanic Province and its significance Curr Sci.
8. Higgins MD, Chandrasekharam D (2007) Nature of Sub-volcanic magma chambers, Deccan
Province, India: evidence from quantitative textural analysis of plagioclase megacrysts in the
giant plagioclase Basalts. J Petrol 48:885–900
9. Ghosh Biswajit, 2011Giant Plagioclase Basalt from Northern Part of Jhabua District, Madhya
Pradesh,Central India. Topics in Igneous Petrology: A Tribute to Professor Mihir K. Bose.
10. Sheth, H. C., Ray, J. S., Senthil Kumar, P., Duraiswami, R. A.,Chatterjee, R. N., Gurav, T., 2011
Recycling of flow-top breccia crusts into molten interiors of flood basalt lava flows: Field and
geochemical evidence from the Deccan Traps. In: Ray, J., Sen, G., Ghosh, B. (Editors), Topics in
Igneous Petrology, pp.161-180. Springer.
11. Valdiya,K.S.,2010,Making of India: A Geodyanamical Evolution
12. http://www.portal.gsi.gov.in/portal/page?_pageid=127,689645&_dad=portal&_schema=PORTAL
13. Rowland SK, Walker GPL (1987) Toothpaste lava: characteristics and origin of a lava
structural type transtional between pahoehoe and aa. Bull Vocanol 49:631–641
14. Ollier C D, Sheth H C 2008The High Deccan duricrusts of India and their significance for
the ‘laterite’ issue